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I rode a steel frame, hub gear bike as commuter for several years and it was fine! 'kick you up into the air and then crash into the ground' was absolutely not my experience. It rode great and shifted fine. I eventually sold it to a mate who is still using it as a commuter 5+ years on
Plenty of happy people on the hub gear bike thread and probably mostly on steel frames too.
Admittedly it was a pompino with a sturmey archer hub and didn't cost anywhere near £1k let alone 3. But still, we're talking about a commuter not a race bike
I would be very careful with dropping that amount of money on a bike that will most likely
ride and shift like shit.
The steel frame will be heavy, the belt drive at that budget limits you to an internal hub so you add essentially an anvil into the rear wheel which will
kick you up in the air and then crash into the ground every time you go over a speed bump.
A gravel setup with drop bars will limit your shifter options unless you go with something
like Alfine Di2.